Rubber composition

ABSTRACT

This invention provides a rubber composition comprising: a softening agent including a hydrogenated naphthenic oil of which an extract quantity of dimethylsulfoxide (DMSO) by IP 346 method is controlled to less than 3% by weight and blending at least one selected from a group of (1) a styrene-butadiene copolymer rubber with a bond styrene quantity in molecular of from 10% by weight to 60% by weight and with a vinyl bond quantity of the butadiene part of from 10% to 80% and (2) a butadiene rubber with a cis bond quantity of at least 30%. The rubber composition is superior in fracture characteristics, loss characteristic and wear resistance, and it is applicable to various rubber products, a pneumatic tire and, in particular, a tire tread.

TECHNICAL FIELD

[0001] This invention relates to a rubber composition. In detail, thisinvention relates to a rubber composition comprising a softening agentcontaining hydrogenated naphthenic oils with less than 3% by weight ofdimethylsulfoxide (DMSO) extract and a synthetic rubber having specifiedmicrostructure, and more particularly, relates to a rubber compositionused for a tire tread.

BACKGROUND ART

[0002] As a softening agent for rubber composition, conventionally ahigh aromatic oil has been broadly employed as a process oil in a fieldof rubber composition for a pneumatic tire or others in a view point ofapplying high loss performance (high heat generating property) oraffinity with rubber. On the other hand, in late years, instead of thearomatic oil, a process oil including less than 3% by weight ofpolycyclic aromatic compounds (PCA) component called as TreatedDistilled Aromatic Extracts (T-DAE), Mild Extracted Solvates (MES) or sobecame to be employed.

[0003] Such a substitute oil, however, has lower softening point thanconventional aromatic oils, and in replacing simply, temperaturedependency of viscoelasticity characteristic of the rubber composition(G′, G″, tan δ) tends to shift toward low temperature side. Therefore,there was a problem that a wet skid resistant performance in an actualtire performance degrades because tan δ value at 0° C. as an indicatorof wet skid performance decreases.

SUMMARY OF THE INVENTION

[0004] Under such situation, an object of this invention is to provide arubber composition particularly for the use to pneumatic tire comprisinga specific softening agent containing less than 3% by weight ofpolycyclic aromatic compounds (PCA) component and besides, withequivalent or superior rupture strength (fracture property) and goodloss characteristic (dynamic loss property) as compared with thearomatic oils.

[0005] In order to overcome the foregoing problem, a rubber compositionblending hydrogenated naphthenic oil of which PCA component iscontrolled to less than 3% by weight with elevated temperature &elevated pressure hydrogenation purification technology having syntheticrubber of various microstructures was provided, and the physicalproperty was evaluated. As a result, it was found effective to blend asoftening agent including specific hydrogenated naphthenic oil with asynthetic rubber having specific microstructure, and this invention wascompleted.

[0006] In other words, this invention provides a rubber compositioncomprising: a softening agent including a hydrogenated naphthenic oil ofwhich an extract quantity of dimethylsulfoxide (DMSO) by IP 346 methodis controlled to less than 3% by weight and at least one selected from agroups of (1) a styrene-butadiene copolymer rubber with a bond styrenequantity in molecular of from 10% by weight to 60% by weight and with avinyl bond quantity of the butadiene part of from 10% to 80% and (2) abutadiene rubber with a cis bond quantity of at least 30%. In addition,this invention provides a tire tread and a pneumatic tire with the useof the foregoing rubber composition.

THE BEST MODE FOR CARRYING OUT THE INVENTION

[0007] In the rubber composition of this invention, styrene-butadienecopolymer rubber (SBR) having a specified microstructure and/or abutadiene rubber (BR) is used as the rubber component blended with theaforementioned particular softening agent. Regarding the SBR, a polymerof which a styrene bond quantity is from 10% by weight to 60% by weight,desirably from 20% by weight to 50% by weight and more desirably from30% by weight to 45% by weight and a vinyl bond quantity in butadienepart is from 10% to 80%, desirably from 10% to 65% is employed. Further,regarding the BR, a polymer of which a cis bond quantity is at least30%, desirably at least 60% and more desirably at least 90% is employed.A manufacturing method of these SBR and BR is not particularly limitedand either an emulsion polymerization method or a solutionpolymerization method is adopted. Considering a balance of variousperformance as a tire tread, however, SBR produced by the emulsionpolymerization method is desirable.

[0008] As a rubber component used for the rubber composition of thisinvention, the aforesaid SBR or BR can be employed by blending a naturalrubber or other dienic rubber, etc. The amount of the SBR or BR in totalrubber component is preferably at least 50% by weight, more preferablyat least 80% by weight and the most preferably 100% by weight becausethe more the amount, the more enough effect is obtained.

[0009] Regarding the softening agent used in this invention, it isrequired to contain a hydrogenated naphthenic oil of which an extractquantity of dimethylsulfoxide (DMSO) by IP 346 method is controlled toless than 3% by weight. Such an oil can be obtained by preparinglyhydrofining a naphthenic oil with elevated temperature & elevatedpressure hydrogenation purification technology, for example. In theforegoing description, IP 346 regulation requires that the amount of PCAcomponent (that is, the extract quantity of dimethylsulfoxide (DMSO) byIP 346 method) must be less than 3% by weight.

[0010] Regarding the kinetic viscosity at 100° C. of the softening agentused in this invention, it is desirable to be up to 350 mm²/second, moredesirable to be up to 200 mm²/second and the most desirable to be up to150 mm²/second from the viewpoint of oil extension to synthetic rubber,workability for blending with the rubber composition (easiness ofintroduction to a kneading machine).

[0011] In addition, an asphalt may be included among the softening agentin this invention. An asphaltene component in the asphalt is desirableto be up to 5% by weight considering miscibility with the syntheticrubber employed or an effect as the softening agent. It is desirablethat such an asphalt is particularly a naphthenic straight asphalt andthat kinetic viscosity at 120° C. of the asphalt is up to 300mm²/second.

[0012] In a softening agent containing asphalt component in thisinvention, a blending weight ratio of the hydrogenated naphthenic oiland the asphalt under the expression of (the hydrogenated naphthenicoil/the asphalt) is desirable to be from 95/5 to 5/95 and more desirableto be from 70/30 to 20/80. Too much asphalt may induce problems incryogenic temperature characteristic, etc. of blended rubber.

[0013] Preparation method for the softening agent containing asphaltcomponent is not particularly limited, and the softening agent preparedeither by mixing the asphalt to hydrogenated naphthenic oil in advanceor by adding major component of the asphalt in appropriate ratio amongthe hydrogenated naphthalenic oil during conventional purificationprocess of hydrogenated naphthenic oil may be employed. However, thepreparation method for the softening agent dissolving the asphalt in thehydrogenated naphthenic oil is desirable in the viewpoint of easiness ofthe preparation or economic reason. These preparation methods for thesoftening agent containing the asphalt component are applicable for thecase where the softening agent is employed either for an extender oil orfor a blending oil.

[0014] In addition, the hydrogenated naphthenic oil has desirably atleast 30% CN of naphthenic hydrocarbon content measured in accordancewith ASTM D2140 (in other word, popular name of ring analysis). Thehydrogenated naphthenic oil with such a characteristic having less than3 weight % of PCA content is available, for example, as SNH8, SNH46,SNH220, and SNH440 (each is a trademark) available from SankyoPetrochemical Co., Ltd.

[0015] The softening agent containing the asphalt of this invention maybe added during the mixing process of the rubber components (includingthe production of masterbatch) or may be added as an extender oil in thepreparation of a synthetic rubber.

[0016] The addition amount of the softening agent to the rubbercomposition of this invention is preferably 1 to 200 parts by weight,more preferably 3 to 150 parts by weight and the most preferably inparticular 5 to 100 parts by weight per 100 parts by weight of therubber component in view of the loss property, fracturing property andwear resistance. The foregoing addition amount of the softening agentmeans total amount of both of the so-called extender oil and blendingoil.

[0017] The addition amount of the softening agent, when used as anextender oil in the production of synthetic rubber, is preferably 5 to150 parts by weight, more preferably 7 to 100 parts by weight and themost preferably in particular 10 to 50 parts by weight per 100 parts byweight of the rubber component (base polymer) being extended. Inaddition, the additional amount of the softening agent, when used as ablending oil in the mixing process of the rubber composition, ispreferably 1 to 70 parts by weight and more preferably 5 to 50 parts byweight per 100 parts by weight of the rubber component. Further, thesoftening agent can be added simultaneously with other fillers orchemicals during its blending.

[0018] A portion of the softening agent containing asphalt that is usedin the rubber composition of this invention may be replaced by anotherconventionally used softening agent. When another softening agent isused, it is preferable that the total blending amount of the softeningagent is within the foregoing range. In order to sufficiently exhibitthe effect of this invention, the softening agent of this invention ispreferably used in an amount of at least 30% by weight of the totalamount of the softening agents including asphaltene-containing softeningagent and another softening agent.

[0019] The rubber composition of this invention may contain areinforcing filler such as carbon black, silica, aluminum hydroxide,etc., in an amount of 20 to 150 parts by weight, preferably 25 to 120parts by weight and more preferably 30 to 105 parts by weight per 100parts by weight of the rubber component.

[0020] There is no limitation in particular as the carbon black, and anycarbon black conventionally used as the reinforcing filler for rubbercan be optionally selected and employed. Typical examples of the carbonblack include FEF, SRF, HAF, ISAF, SAF, etc., and among these, HAF,ISAF, and SAF are desirable because they are particularly superior inwear resistance.

[0021] In addition, there is no limitation in particular as the silica,and any silica conventionally used as the reinforcing filler for rubbercan be optionally selected and employed. Typical examples of the silicainclude wet type silica (hydrate silicic acid), dry type silica (silicicacid anhydride), calcium silicate, aluminum silicate, etc., and amongthese, wet type silica is desirable from the viewpoint of its favorableperformance.

[0022] Further, there is no limitation in particular as the aluminumhydroxide, and the aluminum hydroxides with mean particle size of 10 μmor smaller having the surface processed by surface preparation agent isdesirably employed. By processing the surface of the aluminum hydroxideparticles with the surface preparation agent, the particles particularlywith large diameter among them are prevented from working as breakingkernel and the aggregation between the particles themselves is alsoprevented thereby exhibiting the effect of inhibiting that the aluminumhydroxide aggregate becomes breaking kernel. There is no limitation inparticular as the surface preparation agent, and although any surfacepreparation agent among various conventional agents publicly known canbe optionally selected and employed, silane-based coupling agent andstearic acid are preferable and in particular, silane-based couplingagent is appropriate.

[0023] Furthermore, as a cross-linking agent used for rubber compositionof this invention, any cross-linking agent generally used in the rubberindustry such as organic peroxide, sulfur, and an organic sulfurcompound can be employed. When sulfur or an organic sulfur compound isemployed as the cross-linking agent, a vulcanization acceleratorgenerally used in the rubber industry can be used in the ordinarymanner.

[0024] The rubber composition of this invention may further containinorganic fillers generally used in the rubber industry in an amount of5 to 200 parts by weight, preferably 25 to 120 parts by weight and morepreferably 30 to 105 parts by weight per 100 parts by weight of therubber component in addition to the foregoing components. The rubbercomposition of this invention may further contain other ingredientsgenerally used in the rubber industry such as antioxidants orvulcanization auxiliary agents in addition to the foregoing components.

[0025] This invention will be described in further detail with referenceto Examples, which does not limit the scope of this invention.

[0026] Properties of the asphalt, the softening agents, the hydrogenatednaphthenic oil and rubber compositions were measured in accordance withthe following methods.

Microstructure of Polymer

[0027] A quantity of vinyl bond in conjugated diene unit (a quantity of1,2 bond of butadiene part) was obtained by an infrared method. Inaddition, a quantity of styrene bond in the polymer was obtained by1H-NMR method.

Physical Property Evaluation of the Asphalt and the Softening Agent

[0028] (1) Properties of the Asphalt

[0029] (a) An Asphaltene Component

[0030] The asphaltene component was quantitatively analyzed based on achemical composition analysis measured in accordance with JPI method(Nippon Petroleum Institute method).

[0031] (b) Kinetic Viscosity

[0032] The kinetic viscosity was measured at 120° C. in accordance withJIS K2283-1993.

[0033] (2) Properties of the Hydrogenated Naphthenic Oil

[0034] (a) Measurement of Content of Various Carbon by Ring Analysis

[0035] An aromatic hydrocarbon content (% CA), a naphthenic hydrocarboncontent (% CN) and a paraffinic hydrocarbon content (% CP) each in termsof% by weight in the softening agent were measured in accordance withASTM D-2140.

[0036] (b) Kinetic Viscosity

[0037] The kinetic viscosity was measured at 100° C. in accordance withJIS K2283-1993.

[0038] (c) Aniline Point

[0039] The aniline point was measured in accordance with JIS K2256-1985.

[0040] (d) PCA (Polycyclic Aromatic Compounds)

[0041] PCA was represented by the amount (% by weight) of DMSO extractin accordance with the method of IP 346.

Evaluation of Vulcanized Rubber Composition

[0042] (1) Fracturing Properties

[0043] A test piece was prepared by punching a sheet (150 mm×150 mm×2mm) of vulcanized rubber using a blade of JIS No. 3 in accordance of JISK6301-1995. A breaking strength of the test piece at 25° C. was measuredby means of a tensile testing machine (STROGRAPH AR-1 produced by ToyoSeiki Co., Ltd.) and expressed as an index. The larger the index, thebetter the fracturing properties.

[0044] (2) Loss Property (Dynamic Loss Property)

[0045] The values of tan δ of a vulcanized rubber sheet (5 mm×45 mm×2mm) was measured under conditions of 5% distortion, frequency of 15 Hzat 0° C. and at 60° C. using a viscoelastmeter (RHEOGRAPHSOLID L-1Rproduced by TOYO SEIKI Co., Ltd.).

[0046] The results of the measurement were evaluated by the followingratings:

[0047] a) Regarding the tan δ at 0° C., the measured value was expressedas an index without conducting any calculation. The larger the index,the better the wet skid property.

[0048] b) Regarding the tan δ at 60° C., an inverse value of themeasured value was expressed as an index. The larger the index, thebetter the low fuel consumption property.

[0049] (3) Wear Resistance

[0050] A wear loss at the slip ratio of 60% was measured with theLambourne type wear tester, an inverse value of the measured value wasexpressed as an index. The larger the index, the better the wearresistance. Next, softening agents, specimens for feasibility studies ofnew rubbers, oil extended synthetic rubbers and test pieces ofvulcanized rubber in EXAMPLES and COMPARATIVE EXAMPLES of this inventionwere prepared in the manner described in (A) to (D) below.

(A) Preparation of Softening Agents

[0051] Hydrogenated naphthenic oils shown in Table 1 and heated to 70°C. beforehand were precisely weighed in specified amounts. Naphthenicstraight asphalts shown in Table 2 and heated to 85° C. in order toreduce its viscosity beforehand were precisely weighed in specifiedamounts. Then, while keeping it at 70° C., the straight asphalts wereadded to the hydrogenated naphthenic oils. Thereafter, the mixture wascontinuously stirred for 5 minutes to prepare various softening agentsincluding asphalt. Further, regarding each softening agent used inEXAMPLES and COMPARATIVE EXAMPLES, PCA component (a quantity of DMSOextract) was measured. TABLE 1 Aromatic Hydrogenated Naphthenic oil OilA B C D E Ring Analysis % CA 13.0 15.5 14.0 24.0 44.0 (ASTM D2140) % CN50.0 45.0 27.0 27.0 28.0 % CP 37.0 39.5 59.0 49.0 28.0 Dynamic Viscosity@100° C. (mm²/second) 5.31 12.1 17.00 28.0 24.00 Aniline Point (° C.)74.2 82.6 90.0 80.0 30.0 PCA (% by weight) 2.6 2.6 1.8 2.5 21.4

[0052] TABLE 2 Naphthenic Straight Asphalt Asphalten (% by weight) 0.7Dynamic Viscosity @120° C. (mm²/second) 120

(B) Production of Feasibility Study Rubber (Base Polymer) ProductionExample 1 (SBR-1)

[0053] After purging the content of a pressure proof sealed glass vesselhaving a capacity of 1 litter with nitrogen, 256 g of cyclohexane, 21 gof styrene and 39 g of butadiene were introduced into the vessel. Then,0.11 millimole of ditetrahydrofuryl propane and 0.36 millimole of normalbutyllithium (n-BuLi) were added and polymerization reaction at 50° C.was continued for 3 hours. After 3 hours, 0.5 milliliter of 2-propanolwas added and the reaction was discontinued. A solution dissolving 0.5 gof 2,6-di-t-butyl-p-creosol in 5 milliliter of isopropanol was added asan antioxidant to the foregoing polymer solution. A microstructure ofthe polymer was analyzed about one part of the obtained polymersolution. The results are shown in Table 3.

Production Example 2 (SBR-2)

[0054] After purging the content of a pressure proof sealed glass vesselhaving a capacity of 1 liter with nitrogen, 289 g of cyclohexane, 3 g ofstyrene and 57 g of butadiene were introduced into the vessel. Then,0.55 millimole of ditetrahydrofuryl propane and 0.36 millimole of normalbutyllithium (n-BuLi) were added and polymerization reaction at 50° C.was continued for 3 hours. After 3 hours, 0.5 milliliter of 2-propanolwas added and the reaction was discontinued. A solution dissolving 0.5 gof 2,6-di-t-butyl-p-creosol in 5 milliliter of isopropanol was added asan antioxidant to the foregoing polymer solution. A microstructure ofthe polymer was analyzed about one part of the obtained polymersolution. The results are shown in Table 3.

Production Example 3 (BR-1)

[0055] In a beaker with a capacity of 5 liter, 3 liter of cyclohexaneand 500 g of oil extended high cis polybutadiene “BR31” (trademark;available from JSR Corp.) were introduced and agitated for dissolution.While agitating, this solution was dripped to another beaker with acapacity of 5 liter containing 2 liter of 2-propanol expectingreprecipitation. After vacuum heat drying the polymer from which theextender oil was removed in this way, it was remelted with 3 liter ofcyclohexane in a beaker with a capacity of 5 liter. After fulldissolution, a solution dissolving 0.5 g of 2,6-di-t-butyl-p-creosol in5 milliliter of isopropanol was added. A microstructure of the polymerwas analyzed about one part of the obtained polymer solution. Theresults are shown in Table 3.

Production Example 4 (BR-2)

[0056] A butadiene rubber having 60% of cis bond quantity shown in Table3 was synthesized by conventional method.

Production Example 5 (BR-3)

[0057] Production example 5 was conducted in the same way as Productionexample 3, with the exception of using an oil extended polybutadiene“BUDENE1255” (trademark; available from Goodyear Co., Ltd.) instead ofthe oil extended high cis polybutadiene “BR 31”. A microstructure of thepolymer was analyzed about one part of the obtained polymer solution.The results are shown in Table 3.

Production Example 6 (SBR-3)

[0058] Production example 6 was conducted in the same way as Productionexample 3, with the exception of using an oil extended rubber ofemulsion polymerization styrene-butadiene copolymer rubber “SBR 1712”(trademark; available from JSR Co., Ltd.) instead of the oil extendedhigh cis polybutadiene “BR 31”. A microstructure of the polymer wasanalyzed about one part of the obtained polymer solution. The resultsare shown in Table 3. TABLE 3 Number of Production Example 1 2 6Styrene-Butadien Copolymer Rubber SBR-1 SBR-2 SBR-3 (SBR) Amount of bondStyrene (% by weight) 35 5 23.5 Amount of Vinyl Bond (% 23 75 16 amongButadiene) Notes for Com. EX. Number of Production Example 3 4 5Butadiene Rubber (BR) BR-1 BR-2 BR-3 Amount of Cis Bond (% 95 60 20among Butadiene) Notes for Com. EX.

(C) Preparation of Oil Extended Rubber for Feasibility Study

[0059] A softening agent with a specified composition was added up to37.5 parts by weight to 100 parts by weight of the polymer of SBR or BRpolymer solution obtained after discontinuing polymerization or afterdissolution of reprecipitated materials in Production examples 1 to 6,and the solution was agitated for 30 minutes at 50° C. Various kinds ofoil extended rubbers were obtained after vacuum heat drying thesolution. With regards to the oil extended rubber containing thesoftening agent provided in this way, a description with “oil ext.” in acolumn of Softening Agent Addition Method is done in Tables 5, 6, 8,10and 12.

(D) Preparation of Vulcanized Rubber Test Pieces

[0060] Components for a masterbatch with the formulation shown in Tables4, 7, 9 and 11 were mixed together in a kneader with rollers having asurface temperature of 70° C. and the mixed product was further finallykneaded and was formed into a sheet. The sheet thus obtained was chargedinto a suitable molding die at 160° C. under conditions of a pressure of30 kg/cm², 15 minutes of heating. The vulcanized product was releasedfrom the molding die and test pieces having a predetermined size wereprepared. With regards to the oil extended rubber containing thesoftening agent provided adding the softening agent in the step ofkneading the masterbatch, a description with “knead” in the column ofSoftening Agent Addition Method is done in Tables 5, 6, and 8.

EXAMPLES 1 to 12, COMPARATIVE EXAMPLES 1 to 12 and REFERENCE EXAMPLES 1and 2

[0061] In accordance with formulation shown in Table 4 below, a carbonblack blended SBR or a BR based vulcanized rubber composition wasprepared. TABLE 4 Parts Mixed Stage Blending Contents by wt. BlendedAgent Supplier Masterbatch SBR or BR 100 Base Polymer for feasibilitystudy rubber Kneading N220 Carbon 75 Tokai Siest 6 Tokai Carbon Co.,Ltd. Softening Agent 37.5 Softening Agent as shown in Table 5 StearicAcid 1.5 BR-Stearic Acid Nippon Oils & Fats Co., Ltd. Final Zinc Oxide 3Zinc White No. 1 Hakusui Chemicals Inc. Kneading Sulfur 1.8 SulfurKaruizawa Refinement Co., Ltd. Vulcanization accelerator 1 1.5 NOCCELERDM Ouchi Shinko Chemical Co., Ltd Vulcanization accelerator 2 0.8NOCCELER DPG Ouchi Shinko Chemical Co., Ltd

[0062] Fracture properties, loss properties and wear resistanceregarding the rubber composition were evaluated by the foregoingevaluation methods. The physical property values of the rubbercompositions in EXAMPLES 1 to 12 were expressed by the index valuesmaking the rubber compositions in the corresponding controls andcalculating with fixing the physical property values of the controls as100. The evaluation results are shown in Table 5 (carbon black blendedSBR) and Table 6 (carbon black blended BR). In these Tables, “phr”expresses number of part by weight on the assumption that the polymercomponent corresponds to 100 parts by weight. TABLE 5-1 COM. REF. COM.COM. Carbon Black Blended SBR EX. 1 EX. 1 EX. 1 EX. 2 EX. 2 EX. 3 EX. 3Composition of Hydrogenated SNH46 (phr) — — — — — — — Softening AgentNaphthenic Oil SNH220 (phr) 18.75 18.75 — 37.5 37.5 37.5 37.5 AromaticOil (phr) — — 37.5 — — — — Asphalt as shown in Table 2 (phr) 18.75 18.75— 0 0 0 0 Base Polymer Production Example 1 SBR-1 (phr) — 100 100 — 100— 100 Production Example 2 SBR-2 (phr) 100 — — 100 — 100 — SofteningAgent Addition Method oil ext. oil ext. oil ext. oil ext. oil ext. kneadknead PCA Component in the Softening Agent (DMSO elusion, wt %) 1.3 1.315 0.1 0.1 0.1 0.1 Vulcanization Fracturing Properties FracturingStrength @25° C. (Index) 100 105 105 100 110 100 109 Rubber LossProperty tan δ @0° C. (Index) 100 110 109 100 105 100 105 tan δ @60° C.(Index) 100 100 100 100 100 100 100 Wear Resistance Lambourne AntiwearResistance (Index) 100 110 110 100 105 100 106

[0063] TABLE 5-2 COM. COM. COM. COM. Carbon Black Blended SBR EX. 4 EX.4 EX. 5 EX. 5 EX. 1 EX. 1 EX. 6 EX. 6 Composition of Hydrogenated SNH46(phr) 18.75 18.75 18.75 18.75 — — — — Softening Agent Naphthenic OilSNH220 (phr) — — — — 18.75 18.75 1.5 (4%)  1.5 (4%)  Aromatic Oil (phr)— — — — — — — — Asphalt as shown in Table 2 (phr) 18.75 18.75 18.7518.75 18.75 18.75  36 (96%)  36 (96%) Base Polymer Production Example 1SBR-1 (phr) — 100 — 100 — 100 — 100 Production Example 2 SBR-2 (phr) 100— 100 — 100 — 100 — Softening Agent Addition Method oil ext. oil ext.knead knead oil ext. oil ext. oil ext. oil ext. PCA Component in theSoftening Agent (DMSO elusion, wt %) 1.3 1.3 1.3 1.3 1.3 1.3 0.1 0.1Vulcanization Fracturing Properties Fracturing Strength 100 108 100 107100 105 100 100 Rubber @25° C. (Index) Loss Property tan δ @0° C.(Index) 100 112 100 110 100 110 100 105 tan δ @60° C. (Index) 100 100100 100 100 100 100 99 Wear Resistance Lambourne Antiwear 100 105 100104 100 110 100 99 Resistance (Index)

[0064] TABLE 6-1 COM. REF. COM. COM. Carbon Black Blended SBR EX. 7 EX.7-1 EX. 7-2 EX. 2 EX. 8 EX. 8 EX. 9 EX. 9 Composition of HydrogenatedSNH46 (phr) — — — — 37.5 37.5 37.5 37.5 Softening Agent Naphthenic OilSNH220 (phr) 18.75 18.75 18.75 — — — — Aromatic Oil (phr) — — — 37.5 — —— — Asphalt as shown in Table 2 (phr) 18.75 18.75 18.75 — 0 0 0 0 BasePolymer Production Example 3 BR-1 (phr) — — 100 100 — 100 — 100Production Example 4 BR-2 (phr) — 100 — — — — — — Production Example 5BR-3 (phr) 100 — — — 100 — 100 — Softening Agent Addition Method oilext. oil ext. oil ext. oil ext. oil ext. oil ext. knead knead PCAComponent in the Softening Agent (DMSO elusion, wt %) 1.3 1.3 3 15 0.10.1 0.1 0.1 Vulcanization Fracturing Properties Fracturing Strength @25°C. 100 105 110 109 100 106 100 105 Rubber (Index) Loss Property tan δ@0° C. (Index) 100 101 103 103 100 100 100 100 tan δ @60° C. (Index) 100104 108 107 100 110 100 108 Wear Resistance Lambourne Antiwear 100 105115 117 100 110 100 109 Resistance (Index)

[0065] TABLE 6-2 COM. COM. COM. COM. Carbon Black Blended SBR EX. 10 EX.10 EX. 7 EX. 7-2 EX. 11 EX. 11 EX. 12 EX. 12 Composition of HydrogenatedSNH46 (phr) 18.75 18.75 — — — — 1.5 (4%)  1.5 (4%)  Softening AgentNaphthenic Oil SNH220 (phr) — — 18.75 18.75 18.75 18.75 — — Aromatic Oil(phr) — — — — — — — — Asphalt as shown in Table 2 (phr) 18.75 18.7518.75 18.75 18.75 18.75  36 (96%)  36 (96%) Base Polymer ProductionExample 3 BR-1 (phr) — 100 — 100 — 100 — 100 Production Example 5 BR-3(phr) 100 — 100 — 100 — 100 — Softening Agent Addition Method oil ext.oil ext. oil ext. oil ext. knead knead oil ext. oil ext. PCA Componentin the Softening Agent (DMSO elusion, wt %) 1.3 1.3 1.3 1.3 1.3 1.3 0.10.1 Vulcanization Fracturing Properties Fracturing Strength 100 110 100110 100 109 100 104 Rubber @25° C. (Index) Loss Property tan δ @0° C.(Index) 100 108 100 103 100 104 100 98 tan δ @60° C. (Index) 100 100 100108 100 108 100 104 Wear Resistance Lambourne Antiwear 100 110 100 115100 114 100 105 Resistance (Index)

[0066] According to the result shown in the Tables, the rubbercompositions of this invention are particularly superior in all of thefracture properties, the loss properties (at least one characteristic oftangent δ at 0° C. and tangent δ at 60° C.) and the wear resistanceparticularly when the weight ratio of the (hydrogenated naphthenicoil)/(asphalt) is from 95/5 to 5/95. In addition, by comparing betweenEXAMPLE 2 and EXAMPLE 3, EXAMPLE 4 and EXAMPLE 5, EXAMPLE 8 and EXAMPLE9, EXAMPLE 7 and EXAMPLE 1 1 respectively, it is found that the effectof this invention is obtained either by adding the softening agent tothe oil extended rubber or by adding the softening agent in the step ofkneading the rubber.

[0067] Further, by comparing EXAMPLE 1 and REFERENCE EXAMPLE 1, EXAMPLE7-2 and REFERENCE EXAMPLE 2 respectively, it is found that the rubbercomposition containing carbon black according to this invention showssuperior physical property equivalent to or better than the conventionalrubber composition using an aromatic oil.

EXAMPLES 13 to 18, COMPARATIVE EXAMPLES 13 to 18 and REFERENCE EXAMPLE 3

[0068] In accordance with formulations shown in Table 7 below, aSBR-based vulcanized rubber composition containing silica and carbonblack in combination was prepared. TABLE 7 Parts Mixed Stage BlendingContents by wt. Blended Agent Supplier Masterbatch SBR 100 Base Polymerfor feasibility study rubber Kneading N220 Carbon 20 Tokai Siest 6 TokaiCarbon Co., Ltd. Silica 60 Nipsil AQ Nippon Silica Industry Co., Ltd.Softening Agent 37.5 Softening Agent as shown in Table 5 Silane couplingagent 6 Si69 Degusa Co., Ltd. Stearic Acid 2 BR-Stearic Acid Nippon Oils& Fats Co., Ltd. Antioxidant 1 NOCCLAC6C Ouchi Shinko Chemical Co., LtdFinal Zinc Oxide 3 Zinc White No. 1 Hakusui Chemicals Inc. KneadingSulfur 1.5 Sulfur Karuizawa Refinement Co., Ltd. Vulcanizationaccelerator 1 1 NOCCELER DM Ouchi Shinko Chemical Co., Ltd Vulcanizationaccelerator 2 1 NOCCELER DPG Ouchi Shinko Chemical Co., LtdVulcanization accelerator 3 1 NOCCELER NS-F Ouchi Shinko Chemical Co.,Ltd

[0069] Fracture properties, loss properties and wear resistanceregarding the rubber composition were evaluated by the foregoingevaluation methods. The physical property values of the rubbercompositions in EXAMPLES 13 to 18 were expressed by the index valuesmaking the rubber compositions in the corresponding numbers amongCOMPARATIVE EXAMPLES 13 to 18 as the controls and calculating withfixing the physical property values of the controls as 100. Theevaluation results are shown in Table 8. TABLE 8-1 COM. REF. COM. COM.Silica/Carbon Black Blended SBR EX. 13 EX. 13 EX. 3 EX. 14 EX. 14 EX. 15EX. 15 Composition of Hydrogenated SNH46 (phr) — — — — — — — SofteningAgent Naphthenic Oil SNH220 (phr) 18.75 18.75 — 37.5 37.5 37.5 37.5Aromatic Oil (phr) 13 — 37.5 — — — — Asphalt as shown in Table 2 (phr)18.75 18.75 — 0 0 0 0 Base Polymer Production Example 1 SBR-1 (phr) —100 100 — 100 — 100 Production Example 2 SBR-2 (phr) 100 — — 100 — 100 —Softening Agent Addition Method oil ext. oil ext. oil ext. oil ext. oilext. knead knead PCA Component in the Softening Agent (DMSO elusion, wt%) 1.3 1.3 15 0.1 0.1 0.1 0.1 Vulcanization Fracturing PropertiesFracturing Strength @25° C. (Index) 100 104 104 100 109 100 108 RubberLoss Property tan δ @0° C. (Index) 100 108 107 100 104 100 105 tan δ@60° C. (Index) 100 100 100 100 100 100 100 Wear Resistance LambourneAntiwear Resistance (Index) 100 108 109 100 104 100 103

[0070] TABLE 8-2 COM. COM. COM. Silica/Carbon Black Blended SBR EX. 16EX. 16 EX. 17 EX. 17 EX. 18 EX. 18 Composition of Hydrogenated SNH46(phr) 18.75 18.75 18.75 18.75 — — Softening Agent Naphthenic Oil SNH220(phr) — — — — 1.5 (4%)  1.5 (4%)  Aromatic Oil (phr) — — — — — — Asphaltas shown in Table 2 (phr) 18.75 18.75 18.75 18.75  36 (96%)  36 (96%)Base Polymer Production Example 1 SBR-1 (phr) — 100 — 100 — 100Production Example 2 SBR-2 (phr) 100 — 100 — 100 — Softening AgentAddition Method oil ext. oil ext. knead knead oil ext. oil ext. PCAComponent in the Softening Agent (DMSO elusion, wt %) 1.3 1.3 1.3 1.30.1 0.1 Vulcanization Fracturing Properties Fracturing Strength @25° C.(Index) 100 107 100 106 100 99 Rubber Loss Property tan δ @0° C. (Index)100 110 100 109 100 103 tan δ @60° C. (Index) 100 100 100 100 100 101Wear Resistance Lambourne Antiwear Resistance (Index) 100 106 100 105100 99

[0071] According to the results shown in the Tables, the rubbercompositions of this invention are particularly superior in all of thefracture properties, the loss properties (at least one characteristic oftangent δ at 0° C. and tangent δ at 60° C.) and the wear resistanceparticularly when the weight ratio of the (hydrogenated naphthenicoil)/(asphalt) is from 95/5 to 5/95. In addition, by comparing betweenEXAMPLE 14 and EXAMPLE 15, EXAMPLE 16 and EXAMPLE 17 respectively, it isfound that the effect of this invention is obtained either by adding thesoftening agent to the oil extended rubber or by adding the softeningagent in the step of kneading the rubber.

[0072] Further, by comparing EXAMPLE 13 and REFERENCE EXAMPLE 3, it isfound that the rubber composition containing silica according to thisinvention shows superior physical property equivalent to or better thanthe conventional rubber composition using an aromatic oil.

EXAMPLES 19 to 25, COMPARATIVE EXAMPLES 19 to 25 and REFERENCE EXAMPLE 4

[0073] In accordance with formulations shown in Table 9 below, aBR-based vulcanized rubber composition containing aluminum hydroxide andcarbon black in combination was prepared. TABLE 9 Parts Mixed StageBlending Contents by wt. Blended Agent Supplier Masterbatch SBR or BR100 Base Polymer for feasibility study rubber Kneading N220 Carbon 75Tokai Siest 6 Tokai Carbon Co., Ltd. Alminium Hydroxide 15 HaidilightH-43M Shouwa Denko K. K. Softening Agent 37.5 Softening Agent as shownin Table 5 Stearic Acid 1.5 BR-Stearic Acid Nippon Oils & Fats Co., Ltd.Final Zinc Oxide 3 Zinc White No. 1 Hakusui Chemicals Inc. KneadingSulfer 1.8 Sulfer Karuizawa Refinement Co., Ltd. Vulcanizationaccelerator 1 1.5 NOCCELER DM Ouchi Shinko Chemical Co., LtdVulcanization accelerator 2 0.8 NOCCELER DPG Ouchi Shinko Chemical Co.,Ltd

[0074] Fracture properties, loss properties and wear resistanceregarding the rubber composition were evaluated by the foregoingevaluation methods. The physical property values of the rubbercompositions in EXAMPLES 19 to 25 were expressed by the index valuesmaking the rubber compositions in the corresponding numbers amongCOMPARATIVE EXAMPLES 19 to 25 as the controls and calculating withfixing the physical property values of the controls as 100. Theevaluation results are shown in Table 10. TABLE 10-1 COM. EX. EX. REF.COM. COM. Aluminum Hydroxide/Carbon Black Blended SBR EX. 19 19-1 19-2EX. 4 EX. 20 EX. 20 EX. 21 EX. 21 Composition of Hydrogenated SNH46(phr) — — — — 37.5 37.5 18.75 18.75 Softening Agent Naphthenic OilSNH220 (phr) 18.75 18.75 18.75 — — — — — Aromatic Oil (phr) — — — 37.5 —— — — Asphalt as shown in Table 2 (phr) 18.75 18.75 18.75 — 0 0 18.7518.75 Base Polymer Production Example 3 BR-1 (phr) — — 100 100 — 100 —100 Production Example 4 BR-2 (phr) — 100 — — — — — — Production Example5 BR-3 (phr) 100 — — — 100 — 100 — Softening Agent Addition Method oilext. oil ext. oil ext. oil ext. oil ext. oil ext. oil ext. oil ext. PCAComponent in the Softening Agent (DMSO elusion, wt %) 1.3 1.3 1.3 15 0.10.1 1.3 1.3 Vulcanization Fracturing Properties Fracturing Strength @25°C. 100 105 110 109 100 106 100 110 Rubber (Index) Loss Property tan δ@0° C. (Index) 100 101 103 103 100 100 100 108 tan δ @60° C. (Index) 100104 108 107 100 110 100 100 Wear Resistance Lambourne Antiwear 100 105115 117 100 110 100 110 Resistance (Index)

[0075] TABLE 10-2 COM. COM. COM. COM. Aluminum Hydroxide/Carbon BlackBlended SBR EX. 22 EX. 22 EX. 23 EX. 23 EX. 24 EX. 24 EX. 25 EX. 25Composition of Hydrogenated SNH46 (phr) — — 1.5 (4%)  1.5 (4%)  — — 1.5(4%)  1.5 (4%)  Softening Agent Naphthenic Oil SNH220 (phr) 18.75 18.75— — 18.75 18.75 — — Aromatic Oil (phr) — — — — — — — — Asphalt as shownin Table 2 (phr) 18.75 18.75  36 (96%)  36 (96%) 18.75 18.75  36 (96%) 36 (96%) Base Polymer Production Example BR-1 (phr) — 100 — 100 — 100 —100 3 Production Example BR-3 (phr) 100 100 — 100 — 100 — 5 SofteningAgent Addition Method oil ext. oil ext. oil ext. oil ext. oil ext. oilext. oil ext. oil ext. PCA Component in the Softening Agent (DMSOelusion, wt %) 1.3 1.3 0.1 0.1 1.3 1.3 0.1 0.1 Vulcanization FracturingFracturing Strength 100 110 100 104 100 109 100 103 Rubber Properties@25° C. (Index) Loss Property tan δ @0° C. (Index) 100 103 100 98 100104 100 98 tan δ @60° C. (Index) 100 108 100 102 100 109 100 102 WearResistance Lambourne Antiwear 100 115 100 104 100 113 100 103 Resistance(Index)

[0076] According to the results shown in the Tables, the rubbercompositions of this invention are particularly superior in all of thefracture properties, the loss properties (at least one characteristic oftangent δ at 0° C. and tangent δ at 60° C.) and the wear resistanceparticularly when the weight ratio of the (hydrogenated naphthenicoil)/(asphalt) is from 95/5 to 5/95. Further, by comparing EXAMPLE 19-2and REFERENCE EXAMPLE 4, it is found that the rubber compositioncontaining aluminum hydroxide according to this invention shows superiorphysical property equivalent to or better than the conventional rubbercomposition using an aromatic oil.

EXAMPLES 26 to 33 and COMPARATIVE EXAMPLE 26

[0077] In accordance with formulations shown in Table 11 below, aSBR-based vulcanized rubber composition containing carbon black wasprepared. TABLE 11 Parts Mixed Stage Blending Contents by wt. BlendedAgent Supplier Masterbatch SBR 100 Base Polymer for JSR Co., Ltd.Kneading SBR1712 N220 Carbon 75 Tokai Siest 6 Tokai Carbon Co., Ltd.Softening Agent 37.5 Softening Agent as shown in Table 5 Stearic Acid1.5 BR-Stearic Acid Nippon Oils & Fats Co., Ltd. Final Zinc Oxide 3 ZincWhite No. 1 Hakusui Chemicals Inc. Kneading Sulfur 1.8 Sulfur KaruizawaRefinement Co., Ltd. Vulcanization accelerator 1 1.5 NOCCELER DM OuchiShinko Chemical Co., Ltd Vulcanization accelerator 2 0.8 NOCCELER DPGOuchi Shinko Chemical Co., Ltd

[0078] Fracture properties, loss properties and wear resistanceregarding the rubber composition were evaluated by the foregoingevaluation methods. The physical property values of the rubbercompositions in EXAMPLES 26 to 33 were expressed by the index valuesmaking the rubber compositions in the corresponding numbers amongCOMPARATIVE EXAMPLE 26 as the controls and calculating with fixing thephysical property values of the controls as 100. The evaluation resultsare shown in Table 12. TABLE 12 COM. Carbon Black Blended SBR EX. 26 EX.26 EX. 27 EX. 28 EX. 29 EX. 30 EX. 31 EX. 32 EX. 33 Composition ofHydrogenated C in Table 1 (phr) 0 1.5 (4%)  11.25  36 (96%) 37.5 — — — —Softening Naphthenic Oil D in Table 1 (phr) — — — — — 1.5 (4%)  13.1  36(96%) 37.5 Agent Asphalt as shown in Table 2 (phr) 37.5  36 (96%) 26.251.5 (4%)  0  36 (96%) 24.4 1.5 (4%)  0 Base Polymer Production SBR-3(phr) 100 100 100 100 100 100 100 100 100 Example 6 Softening AgentAddition Method oil ext. oil ext. oil ext. oil ext. oil ext. oil ext.oil ext. oil ext. oil ext. PCA Component in the Softening Agent 0 0.10.5 1.7 1.8 0.1 0.9 2.4 2.5 (DMSO elusion, wt %) VulcanizationFracturing Fracturing 100 99 101 98 98 99 99 98 98 Rubber PropertiesStrength @25° C. (Index) Loss Property tan δ @0° C. 100 98 93 84 83 9592 84 83 (Index) tan δ @60° C. 100 106 122 122 122 122 122 122 122(Index) Wear Lambourne 100 101 111 105 105 102 112 106 105 ResistanceAntiwear Resistance (Index)

[0079] According to the results shown in the Tables, the rubbercompositions of this invention using the softening agents with theweight ratio of the (hydrogenated naphthenic oil)/(asphalt) is from 95/5to 5/95 in EXAMPLES 27 and 31 are superior in all of the fractureproperties, the loss properties (at least one characteristic of tangentδ at 0° C. and tangent δ at 60° C.) and the wear resistance and acombination effect of the hydrogenated naphthenic oil and the asphalt isclearly recognized.

INDUSTRIAL APPLICABILITY

[0080] According to this invention, by blending a softening agentcontaining less than 3% by weight of PCA component includinghydrogenated naphthenic oil and SBR or BR of a specified microstructure,a rubber composition superior in fracture characteristics, losscharacteristic and wear resistance is provided as the foregoingdescription. In addition, this invention also provides a rubbercomposition showing equivalent or superior physical property with aconventional rubber composition using an aromatic oil. Therefore, thisinvention can be applicable to various rubber products, a pneumatic tireand, in particular, a tire tread.

What is claimed is:
 1. A rubber composition comprising: a softeningagent including a hydrogenated naphthenic oil of which an extractquantity of dimethylsulfoxide (DMSO) by IP 346 method is controlled toless than 3% by weight, and blending at least one selected from a groupof (1) a styrene-butadiene copolymer rubber with a bond styrene quantityin molecular of from 10% by weight to 60% by weight and with a vinylbond quantity of the butadiene part of from 10% to 80% and (2) abutadiene rubber with a cis bond quantity of at least 30%.
 2. The rubbercomposition according to claim 1, wherein said bond styrene quantity inmolecular of the styrene-butadiene copolymer rubber is from 20% byweight to 50% by weight.
 3. The rubber composition according to claim 1or claim 2, wherein said vinyl bond quantity of the butadiene part ofthe styrene-butadiene copolymer rubber is from 10% to 65%.
 4. The rubbercomposition according to any one of claims 1 to 3, wherein said cis bondquantity of the styrene-butadiene copolymer rubber is at least 60%. 5.The rubber composition according to any one of claims 1 to 4, whereinsaid hydrogenated naphthenic oil has at least 30% CN of naphthenichydrocarbon content measured in accordance with ASTM D2140.
 6. Therubber composition according to any one of claims 1 to 5, wherein saidsoftening agent further contains asphalt with up to 5% by weight of anasphaltene component.
 7. The rubber composition according to any one ofclaims 1 to 6, wherein a kinetic viscosity at 120° C. of said asphalt isup to 300 mm²/second.
 8. The rubber composition according to claim 6 orclaim 7, wherein a blending weight ratio of the hydrogenated naphthenicoil and the asphalt under the expression of (the hydrogenated naphthenicoil/the asphalt) in said softening agent is from 95/5 to 5/95.
 9. A tiretread with the use of the rubber composition according to any one ofclaims 1 to
 8. 10. A pneumatic tire with the use of the rubbercomposition according to any one of claims 1 to 8.